Yeah, the older (60s) cabs were just guitar cabs with almost the same speakers in them (stamped frame Celestions with either heavier or the same guitar cones but coated - to to provide stiffness and lower resonance).
They later used actual bass drivers (not sure exactly what) in the 'bass' 4x12s and had a larger volume to match as GoT says, but the old 4x15s used some sweet cast frame Celestions. I'd love to try one of those sometime.
They also used Goodman drivers at some point and I know I really like those - you can get those in a 12" (even though Marshall didn't use the 12s as far as I know, which is not far) and they'd be a good candidate for your project I think.
If you do get an empty 4x12 and put bass drivers in there - definitely stuff the cab as it'll match the drivers better and help damp internal resonances. You'll have to play with stuffing density to get it right -what ever that is for you.